The present invention is an shaft and bearing assembly. Although the present invention is disclosed in the context of particular power tools, it is not limited to such applications.
When an assembly comprising a ball bearing is fitted onto a shaft, it is typically assembled onto the shaft by press fitting or otherwise assembling the assembly from one end of the shaft. It is then often necessary to provide a mechanism for preventing the bearing assembly from coming off the shaft end over which it was originally placed. In many instances, it is important that the mechanism used not only provide a safe and dependable restraint but also take a minimum of space next to the bearing assembly. It is also of interest from a cost standpoint to minimize the total number of parts used.
Several attempts at such restraints have been previously tried. For example, U.S. Pat. No. 4,854,085 illustrates the use of a snap ring 60 for holding together an output shaft and bearing assembly. A major disadvantage of such a restraint is its inclination to break. U.S. Pat. No. 4,056,291 uses a conventional hub and set screw to hold a clutch housing and bearing assembly onto its drive shaft 70, as shown in FIG. 8 of the patent. Such a conventional hub and set screw requires considerable volume and depends upon the tightness of the set screw for securing the assembly. U.S. Pat. No. 4,516,358 discloses use of a lock ring 30 which retains spindle 22 and bearings 26 within the confines of housing 14, as is discussed in column 3 at lines 51-54 of the patent. As with the snap ring 60 disclosed in U.S. Pat. No. 4,854,085, the lock ring disclosed in U.S. Pat. No. 4,516,358 is inclined to break. Further, such snap or lock rings, if placed at the end of a shaft, result in a restraining mechanism that requires substantial volume, since the shaft must extend beyond the snap or lock ring in order to hold the ring in place. U.S. Pat. No. 3,496,680 discloses use of a retaining ring 42, the outer edge portion of which bears annularly and upwardly against the inner race 38 of a ball bearing, with a screw 40 being used to hold retaining ring 42 in place. Accordingly, this method of attachment is also conventional, with the same inclination of ring 42 to break, take up valuable space, and add to the cost of the product. Other possible approaches of restraining a bearing assembly onto a shaft includes a simple press fit, which is much less safe, and a split output shaft with tapered threads in the end of the shaft, this approach having the potential problem of developing too much pressure on the press fit inside the bearings, thus developing excessive heat during tool operation.
The present invention overcomes the prior art problems discussed above and provides a safe restraint for retaining a bearing assembly onto a shaft at one end of the shaft while occupying minimum space at the end of the shaft without disturbing the functional properties of the bearing and without the cost of an additional part such as a snap ring.